The present invention relates generally to a structure for supporting electronic component carriers, such as printed circuit cards, in a chassis, such as an enclosure.
It has been common practice for many years to mount printed circuit boards or cards in enclosures as so called plug-in units that may be easily inserted into and/or removed from the enclosure for replacement or repair. Conventionally, the plug-in units are slidably received in guide and support structures that are commonly named board guides or board rails. The main purpose of the board guide is to securely guide the plug-in unit into position in the enclosure, so that it may be connected to the backplane of the enclosure. In its simplest form, the conventional board guide typically consists of a molded guide channel manufactured from a non-conductive material and having integrally formed attachment means.
However, for most applications board guides are presently required to establish electrical contact between a conductive pattern or layer on the printed circuit board or card and a wall of a conductive enclosure. Such electrical contact or connection may be required both for the purpose of employing the enclosure as ground for the operation of the separate circuit boards and/or electronic components carried thereon and for the purpose of eliminating or at least minimizing electromechanical radiation emanating from the boards or cards.
Several attempts have been made to develop board guide structures that will meet the requirements for establishing an electrical connection between the circuit boards and the enclosure. Typically, such further developed board guides have a composite structure consisting of a solid channel member accommodating a separate contact and/or guide member. The solid channel member is normally molded or extruded from a synthetic resin material and accommodates a contact and/or guide member having several board contact spring fingers formed of a conductive metal. The contact and/or guide member is also provided with integral enclosure contact means extending through openings in the channel member to contact the enclosure. In other arrangements the channel member is formed of a thermally conductive material, such as aluminum, in order to promote heat transfer from the circuit board.
Examples of such prior art composite board guides are disclosed in U.S. Pat. Nos. 5,187,648, 5, 805,429 and 5,533,631.
U.S. Pat. No. 4,007,403 discloses a board guide that is formed as an integral unit of for instance stainless steel. Accordingly, this board guide eliminates some of the above discussed disadvantages. On the other hand, it comprises very few board contact points, which means that a reliable electrical contact with an inserted circuit board cannot be guaranteed.
In the board guides of the above discussed general designs it is difficult to provide a reliable electrical contact between the board and the enclosure and to maintain such contact during the useful life of the board guide. For the composite design, the reason for this is mainly the separate channel members and contact members. Specifically, the channel member is typically attached to the enclosure and the enclosure contact means of the guide and/or contact member are clamped between the channel member and the enclosure by said attachment. This means that cold flow or aging of the channel member material will directly affect the electrical connection that is basically also rather unreliable due to the fact that the contact is established only at the individual contact points of the board contact fingers and of the enclosure contact means. In this regard, the board guide design disclosed in U.S. Pat. No. 4,007,403 is even more unreliable. Here, the electrical contact between the board and the enclosure is restricted to the attachment means at the two ends of the structure, leaving the entire middle area of the structure free of any positive attachment to a supporting enclosure.
For the same reason the heat transfer capacity of the conventional board guide designs is quite limited, especially where the channel member consists of a resin material. In such board guides, the transfer of heat from the circuit board is restricted mainly to the limited contact points of the guide and/or contact member. Even in the above mentioned structures where the channel member is formed as an extruded aluminum profile or as an integral unit of stainless steel, the transfer of heat from the board to the channel member is restricted by the limited contact points. In the composite design heat transfer is also restricted even further by the often casual transfer from the guide and/or contact member to the channel member.
Furthermore, the conventional board guides cause additional problems in applications involving air-cooled enclosures. In such applications, cooling air flows through perforations in the enclosure walls to remove heat from the mounted circuit boards. In the above discussed conventional board guides a considerable portion of the flow of cooling air is effectively blocked by the guide structures having a rigid base forming or supporting the channel or channel member, respectively. The composite structure with the solid channel member as well as the integral guide structure of U.S. Pat. No. 4,007,403, are also both comparatively wide, so that they cover and thus block a relatively large number of perforations. In view thereof, the use of such board guide designs necessitates the use of more powerful fans to produce the required cooling-air flow through the walls of the enclosure.
The invention overcomes the above problems in an efficient and satisfactory manner.
A general object of the invention is to provide a solution to the problem of providing an effective guide and support structure for a plug-in unit that is intended for slidable insertion into a chassis.
In particular, it is an object of the invention to provide an improved guide and support structure that enhances the removal of heat from an inserted plug-in unit, in addition to maintaining a secure and stable guide and support for the plug-in unit and good electric contact properties.
Briefly, this is achieved by means of a guide and support structure having an upper web forming a guide channel for a plug-in unit. Through side walls of the structure, the upper web is connected to a base of the structure. With such a configuration the guide and support structure will be slim and will basically not cause any unnecessary blockage of a cooling-air flow in a supporting chassis. Moreover, the base is at least partially open in order to allow air flow through the interior of the structure. Such a partly open design of the base will additionally reduce blockage of the cooling-air flow. This reduction of the blockage of cooling-air flow will in turn enhance the cooling of the plug-in units and will require less powerful fans for producing the cooling-air flow.
In an embodiment of the invention, the guide and support structure is formed as an integral unit from an electrically as well as thermally conductive metallic plate material. The metallic plate material will not only provide the appropriate support and guide for the plug-in unit, but will also secure good electrical contact throughout the useful life of the structure.
In another embodiment of the invention, the base of the guide and support structure has means for fixing the structure against the chassis as well as means for establishing electrical contact with the chassis. With such a configuration, good electric contact will be established both with regard to the chassis and to the plug-in unit.
In another embodiment of the invention the guide and support structure is configured as an elongated profile having a base forming means for conducting heat from a plug-in unit to the chassis. By virtue of the metallic material, the guide and support structure will also act as an effective heat sink.
In a practical embodiment the base of the guide and support structure is formed by free edges of the side walls, said free edges serving to support the structure against a chassis wall and to fix the structure to said wall as well as to provide the desired electrical and heat conducting contact therewith. Leaving the entire space between the side wall edges open will provide maximum cooling-air flow into the interior of the profile.
In a further embodiment of the invention the pressure drop of the cooling air flow caused by the guide and support structures of a chassis is reduced even further by providing apertures in at least one of the side walls of the elongated profile, said apertures serving to form a path for the cooling-air flow from the interior of the elongated profile to the interior of the chassis.
In other embodiments of the invention the guide and support structure is designed to provide a particularly secure guiding of the plug-in unit into position and a particularly firm support of said plug-in unit in a fixed position, and to provide a particularly effective electrical contact between the plug-in unit and the guide and support structure.
In further embodiments of the invention, the guide and support structure is designed to provide possibilities for a rational manufacturing of the integral guide and support structure, and to provide a secure attachment of the entire guide and support structure to a chassis wall.
These and further objects of the invention are met by the invention as defined in the appended patent claims.
In summary, the present invention provides the following advantages over the state of the art:
A good electrical contact will be maintained at all times; thereby
Securing a reliable grounding of the plug-in unit; and
An effective shield against electromagnetic radiation;
The guide and support structure will secure an effective conduction of heat from the plug-in unit, acting as a heat sink;
The guide and support structure causes minimum blockage of a cooling air flow, thereby further enhancing cooling of the plug-in unit;
The plug-in unit will be securely guided and supported in the structure;
The support unit is extremely easy to handle and to mount, consisting of only one unitary piece.
Other advantages offered by the present invention will be readily appreciated upon reading the below detailed description of embodiments of the invention.